Foam production is detrimental to the efficiency of many industrial processes that utilize aqueous solutions or suspensions. Many typical defoaming agents which are commonly employed control foam during these processes but may lead to deposition on process equipment requiring a costly clean up of the equipment and inconvenient down time. Examples of processing where foam is detrimental, and insoluble material deposition is common include, but are not limited to, paper manufacturing, paper deinking, textile processing, mining and sewage disposal systems. The insoluble defoaming particle may actually deposit upon the surface of the substrate being processed causing the processed substrate to be of inferior quality, thereby requiring additional removal. This results in increased costs to the manufacturer.
In the paper industry the Kraft process is one of the most frequently used alkaline pulping processes. It is valuable in that spent chemicals may be recycled and reused thus decreasing processing costs. A large disadvantage of this process is the occurrence of foam during the pulp screening and washing procedures.
The Kraft process as taught in U.S. Pat. No. 3,215,635 (Liebling) is generally described as being performed by first cooking the wood chips in digesters and then drawing off the spent chemicals for reuse. The resulting pulp fibers are then washed free of a large amount of chemicals in brown stock washers. These washers are a series of vats, usually three or four in number, which alternatively dilute the pulp with water and thicken it by picking it up on large rotary screens. From the brown stock washers, the pulp travels to the screen room where it is again diluted with water and put through vibrating screens which accept the now completely deliginified fibers and reject the clumps of unpulped fibers, knots and other foreign material. Foam problems are severe in the screen room since the pulp is subjected to violent agitation by the screens. The water removed from the pulp after the screening operations is referred to as dilute black liquor and, for the sake of economy, is normally used for dilution water for the third and fourth stage of the brown stock washers. The dilute black liquor is the foaming material, containing from about 0.001% to 0.1% by weight of solids and has a pH of about 12. The foaming of the dilute black liquor increases with the increase of the resin content of the wood used in this process.
Defoamers are generally used in most alkaline pulp mills during the screening operations so that a more efficient screening is accomplished and to prevent the pulp thickeners, utilized after the screening operations, from becoming clogged with entrapped air. The control or elimination of foam in the screening operation contributes to the overall washing of the pulp during the alkaline pulping process. This is accomplished by the fact that the screening efficiency of the pulp is increased, allowing ease of flow of the pulp throughout the thickeners and subsequent washers.
The mining industry also consumes defoamers. Flotation schemes, both reverse and aerated, separate finished products from known contaminates in the system by saponifying ions in the system and generating foam using saponified fatty acid.
The present defoamers that are used in alkaline pulp mills and in the mining industry often do not control foaming to a satisfactory extent. Consequently, there is need for new defoamers that control the production of foam to a greater extent than the present commercial defoamers.